Project description:Biological nitrogen fixation, the microbial reduction of atmospheric nitrogen to bioavailable ammonia, represents both a major limitation on biological productivity and a highly desirable engineering target for synthetic biology. However, the engineering of nitrogen fixation requires an integrated understanding of how the gene regulatory dynamics of host diazotrophs respond across sequence-function space of its central catalytic metalloenzyme, nitrogenase. Here, we interrogate this relationship by analyzing the transcriptome of Azotobacter vinelandii engineered with a phylogenetically inferred ancestral nitrogenase protein variant. The engineered strain exhibits reduced cellular nitrogenase activity but recovers wild-type growth rates following an extended lag period. We find that expression of genes within the immediate nitrogen fixation network is resilient to the introduced nitrogenase sequence-level perturbations. Rather the sustained physiological compatibility with the ancestral nitrogenase variant is accompanied by reduced expression of genes that support trace metal and electron resource allocation to nitrogenase. Our results spotlight gene expression changes in cellular processes adjacent to nitrogen fixation as productive engineering considerations to improve compatibility between remodeled nitrogenase proteins and engineered host diazotrophs. IMPORTANCE Azotobacter vinelandii is a key model bacterium for the study of biological nitrogen fixation, an important metabolic process catalyzed by nitrogenase enzymes. Here, we demonstrate that compatibilities between engineered A. vinelandii strains and nitrogenase variants can be modulated at the regulatory level. The engineered strain studied here responds by adjusting the expression of proteins involved in cellular processes adjacent to nitrogen fixation, rather than that of nitrogenase proteins themselves. These insights can inform future strategies to transfer nitrogenase variants to non-native hosts.
Project description:Comparison of Azotobacter vinelandii str. DJ transcriptomes using either ammonium or dinitrogen as sole nitrogen source. Transcriptomes from cells in early stages of nitrogenase derepression (10 min and 30 min) and at the peak of nitrogenase derepression (4 hours) were compared against the corresponding controls from cells using ammonium as nitrogen source. Kinetics of the nitrogen fixation (nif) genes expression profiles resemble those previously published (Poza-Carrion, 2013; doi: 10.1128/jb.00942-13).
Project description:The enhancer binding protein VnfA1 of Azotobacter vinelandii has two paralogs as well VnfA2 and VnfA3. This experiment was carried out to compare the binding sites of VnfA1 and VnfA3 under conditions of vanadium availability and its absence. This is important for the regulation of expression of alternative nitrogenase isoenzymes in response to metal availability.
Project description:The transcriptional differences found during stationary-phase ammonium accumulation show a strong contrast between the deregulated (nifL disrupted) and wild-type strain, and to what was reported for the wild-type strain under exponential growth related to key processes involved in driving the process of nitrogen fixation in A. vinelandii. These results further illuminate a number of additional genes associated with siderophore synthesis, molybdate transfer and electron transfer that are likely associated with biological nitrogen fixation.
